Wiring Inside Structural Tube Steel

[aforni]

A new patio shade structure is framed in 2"x3" structural tube steel. It's welded together and supported from the front facade of the building.

The architect requests to route wiring inside the tube steel. It would enter the steel at the building wall, then make 90s down to a vertical member, then turn another 90 thru a threaded nipple. It would then power a small LED luminaire head - see detail.

My questions:

1. Is this code compliant? Since it's not in a listed raceway I was assuming to use cable, perhaps MC or SO (Article 400). Can you think of any code concerns?
2. Is this buildable? I was thinking the sharp edges of the weld could damage the pull, assuming you could actually fish it thru. Maybe installing a jbox at the top of the vertical member would be much better - this way there's only one 90, i.e. the last bend thru the threaded nipple in the detail.

The wiring will probably be low voltage (12V) but I'm curious if you see any difference with line voltage.

Thanks for your thoughts - I'm just a stupid engineer and don't have the field experience of your smart minds. As always, code references are appreciated.

 

[petersonra]

I don't see how anyone could object to MC as long as it was Ok for wet areas.

I don't think cord would be acceptable, at least code wise.

 

[iwire]

No way on SO or single conductors.

It would have to be a cable like UF or MC for wet locations.

 

[GoldDigger]

No way on SO or single conductors.

It would have to be a cable like UF or MC for wet locations.

Since you will have a 12V transformer remotely located this may allow the wiring inside the tube to be Class 2. If so landscape cable might also work. Find out whether the transformer is officially listed as a Class 2 power source, or if such a transformer can be used. It would simplify things greatly.

 

[Noodles]

+1 on land scape cable. check out Q-Tran cables for low voltage and some limited line voltage. some of them are rated for all sorts of insallations. They even have their own water tight termination connectors. We used a bunch of this and PVC coated M/C in hollowed out cedar beams and metal tubing on a high end custom home where we had to hide everything!
http://www.q-tran.com/q-wire

 

[renosteinke]

90.4 makes clear that the NEC is there to support the AHJ, not to take his place. The AHJ can rule as he wishes- after all, he IS the authority. This application is a classic example of where the AHJ may use his discretion.

Not a listed raceway? Not a problem. The AHJ might review the various standards for various raceways, and ask himself "IF this assembly was sent to UL, would it pass muster?" Then, the plan is treated as if it were an appliance.

There are four primary areas of of concern:
1) Is the metal tube equal to, or better than, the listed product in how it protects the wires?;
2) Is the interior free of burrs, essentially 'smooth,' as is expected of welded tube conduit?;
3) Is there enough bending space for the wires?; and,
4) Are the wires protected from strain and abrasion where they enter and exit the tubing?

Voltage DOES matter. Both NEC and listing rules change quite a bit over 50 volts. It's amazing what is allowed for 'low voltage' stuff.

 

[iwire]

90.4 makes clear that the NEC is there to support the AHJ, not to take his place. The AHJ can rule as he wishes- after all, he IS the authority. This application is a classic example of where the AHJ may use his discretion.

Absolutely untrue unless they have amendments.

 

[aforni]

Thank you very much for the excellent responses.